Object approach detection device and object approach detection method

ABSTRACT

An object approach detection device includes: an imager that includes a first and a second lens group which have different focal lengths from each other and are arranged so as to image a same target object and that acquires first and second image information imaged through the first and the second lens group, respectively; an object detector that detects presence or absence of an object; and an object approach determiner that determines that approach of the object has been detected when a time difference between a first time and a second time is equal to or less than an approach determination threshold value, the first time being when the first image information is acquired when the object has been detected based on the first image information, the second time being when the second image information is acquired when the object has been detected based on the second image information.

The entire disclosure of Japanese patent Application No. 2017-032991,filed on Feb. 24, 2017, is incorporated herein by reference in itsentirety.

BACKGROUND Technological Field

The present invention relates to an object approach detection device andan object approach detection method.

Description of the Related Art

Conventionally, as a detection device or a detection method of anapproaching object, there has been known one that detects a surroundingobject by using a stereo camera or the like and measures the distance tothe object.

Moreover, JP 2014-16309 A discloses a device which uses a lens unitconstituted by a main lens and a lens array, in which microlenses whosefocal lengths can be varied are two-dimensionally arranged, to estimatethe distance based on image information corresponding to each focallength.

JP 2014-62748 A discloses a device which uses a multifocal lens having aplurality of focusing lengths to capture an image simultaneously foreach of the plurality of focusing lengths to acquire a plurality ofimages, and detects a position of a moving object in a three-dimensionalspace based on the plurality of acquired images.

In the device described above in JP 2014-16309 A, the distanceestimation is performed based on the image information corresponding toeach focal length so that the amount of the calculation for this becomeslarge, and the power consumption increases.

Moreover, in the device in JP 2014-62748 A, the focal length that bestfocuses from image information on the plurality of focal lengths, thatis, a distance z to the object is estimated and calculated, and the xyposition of the object is detected based on this to obtain thethree-dimensional position (x, y, z) of the object. Furthermore, thethree-dimensional position is detected at each predetermined time toobtain a movement locus of the object. Thus, the amount of thecalculation also becomes large, and the power consumption increases.

In recent years, a detection device which detects the approach of anobject is also mounted on a small flying machine such as a drone, andthus prevention of a crash due to collision has been intended.

In this small flying machine, it is necessary to detect an approachingobject at a wide angle over a wide range in order to detect objects fromvarious directions. However, in order to detect an approaching object ata wide angle, a plurality of cameras are necessary. In a case where astereo camera is used, the number of camera modules increases, theweight increases, and the flight time becomes short.

Thus, although a monocular system can be considered, focusing isnecessary for distance measurement of an approaching object, andfocusing takes time so that images cannot be acquired at the same time.Moreover, since a focusing lens and a driving mechanism are necessary,the lens becomes heavy, and the flight time becomes short.

Furthermore, as described above, the amount of the calculation becomeslarge, and the power consumption increases in the ones that estimate thedistance to the object. In addition, the flight time becomes short in asmall flying machine with a limited power source capacity.

SUMMARY

The present invention has been made in light of the above problems, andan object of the present invention is to provide an object approachdetection device and the method thereof, which can reduce the amount ofcalculation for detecting an approaching object and reduce powerconsumption.

To achieve the abovementioned object, according to an aspect of thepresent invention, an object approach detection device reflecting oneaspect of the present invention comprises: an imager that includes afirst lens group and a second lens group which have different focallengths from each other and are arranged so as to image a same targetobject and that acquires first image information and second imageinformation imaged through the first lens group and the second lensgroup, respectively; an object detector that detects presence or absenceof an object based on the first image information and the second imageinformation; and an object approach determiner that determines thatapproach of the object has been detected when a time difference betweena first time and a second time is equal to or less than an approachdetermination threshold value, the first time being when the first imageinformation is acquired when the object has been detected based on thefirst image information, the second time being when the second imageinformation is acquired when the object has been detected based on thesecond image information.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of theinvention will become more fully understood from the detaileddescription given hereinbelow and the appended drawings which are givenby way of illustration only, and thus are not intended as a definitionof the limits of the present invention:

FIG. 1 is a diagram showing the schematic configuration of an objectapproach detection device according to an embodiment of the presentinvention;

FIG. 2 is a diagram showing an example of the functional configurationof an object detector;

FIG. 3 is a block diagram showing the hardware configuration of theobject approach detection device;

FIG. 4 is a diagram showing another example of the lens configuration ofan imager of the object approach detection device;

FIG. 5 is a diagram showing still another example of the lensconfiguration of the imager of the object approach detection device;

FIG. 6 is an enlarged view showing one lens in the imager shown in FIG.5;

FIG. 7 is a diagram showing a schematic flow of a series of processingin a processing unit of the object approach detection device;

FIGS. 8A and 8B are diagrams showing examples of image information andedge images in the object approach detection device;

FIGS. 9A to 9C are diagrams show how an object is detected from theimage information;

FIGS. 10A and 10B are diagrams showing a schematic flow of a series ofprocessing in an object approach determiner;

FIG. 11 is a diagram showing how the approach of the object is detectedby dividing a region of image information;

FIG. 12 is a diagram showing an example of determining the approach tobe not detected even an object is detected; and

FIG. 13 is a flowchart showing a schematic flow of a series ofprocessing in the object approach detection device.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, one or more embodiments of the present invention will bedescribed with reference to the drawings. However, the scope of theinvention is not limited to the disclosed embodiments.

FIG. 1 shows the schematic configuration of an object approach detectiondevice 1 according to an embodiment of the present invention. FIG. 2 isa diagram showing an example of the functional configuration of anobject detector 23. FIG. 3 shows an example of the hardwareconfiguration of the object approach detection device 1.

In FIG. 1, the object approach detection device 1 has an imager 10 and aprocessing unit 20.

The imager 10 includes a main lens 11, a first lens group 13G and asecond lens group 14G which have different focal lengths from each otherand are arranged so as to image the same target object and, and acquiresfirst image information D1 and second image information D2 imagedthrough each of the main lens 11, the first lens group 13G and thesecond lens group 14G.

The main lens 11 is for collecting light, expanding the target range ofthe imaging and enlarging the viewing angle (widening angle).

The first lens group 13G is a lens array including a plurality of firstlenses 13, 13 and so on having a first focal length. The second lensgroup 14G is a lens array including a plurality of second lenses 14, 14and so on having a second focal length.

The plurality of first lenses 13, 13 and so on and the plurality ofsecond lenses 14, 14 and so on are arranged on one object plane 12. Inthis example, the object plane 12 is flat and may be a transparentobject such as glass or may be a virtual plane. Alternatively, theobject plane may be curved instead of being flat.

The imager 10 further has a first imaging element 16S which receives thelight having passed through the first lens group 13G and outputs thefirst image information D1 and a second imaging element 17S whichreceives the light having passed through the second lens group 14G andoutputs the second image information D2. The first imaging element 16Sand the second imaging element 17S include imaging elements 16 and 17corresponding to the lenses 13 and 14, respectively, and synthesizes thefirst image information D1 and the second image information D2 for eachfocal length based on the images captured by these elements.

The first imaging element 16S and the second imaging element 17S arearranged to face the object plane 12. That is, they are arranged along aflat imaging plane 15 facing the object plane 12. Note that, although apart of the imaging plane 15 is the first imaging element 16S and thesecond imaging element 17S herein, it is also possible to use the entireimaging plane 15 as an imaging element and extract a necessary part ofimage information to be synthesized.

Note that the first lens group 13G is a lens group with a long focusinglength L and the second lens group 14G is a lens group with a shortfocusing length L in the present embodiment. Suppose that the focusinglength of the first lens group 13G is L1 and the focusing length of thesecond lens group 13G is L2. Then, L1 is longer than L2, L1>L2. That is,the first focal length of the first lenses 13 is longer than the secondfocal length of the second lenses 14.

Therefore, the first lenses 13 focus on a more distant object and thesecond lenses 14 focus on an object closer than the case of the firstlenses 13. Thus, in a case where the object approaches the imager 10from a long distance, the first image information D1 focused by thefirst lens group 13G is acquired first, and the second image informationD2 focused by the second lens group 14G is acquired thereafter.

Imaging is performed continuously, that is, periodically by the imager10 at predetermined time intervals for a target range of a predeterminedviewing angle, and the first image information D1 and the second imageinformation D2 are acquired at the respective timings. At this time,time stamps (digital time stamps) DTS indicating the timings of imagingare acquired. The time stamp DTS indicates a time t at which each of thefirst image information D1 and the second image information D2 isacquired. As an example of the time t, it can be shown as “Jan. 30, 201713:10:25 27,” “15:52:18 78,” “17:21:25:66,” or the like.

The time interval of the imaging at the imager 10 can be, for example,1/60 seconds, 1/30 seconds, 1/10 seconds, one second, two seconds, orthe like. In a case where it is desired to increase the speed of objectapproach detection, the time interval may be short. In a case where thespeed of the detection may be slow, the time interval may be long.Moreover, a moving image with an appropriate frame rate such as 60frames per second (fps), 30 fps or 25 fps may be acquired, and stillimages and the like may be extracted from the moving image.

As the imager 10, it is possible to use a camera or a video camera inwhich a lens, an imaging element and the like are integrally formed. Theimage information D1 and D2 to be acquired may be RGB color imageinformation or may be monochrome image information, infrared orultraviolet ray image information, or other image information.

The processing unit 20 has image storage 21 and 22, an object detector23 and an object approach determiner 24.

The image storage 21 and 22 respectively store the first imageinformation D1 and the second image information D2 acquired andtransferred by the imager 10.

The object detector 23 detects the presence or absence of an objectbased on the first image information D1 and the second image informationD2.

As shown well in FIG. 2, the object detector 23 has, for example, anedge detector 231 that performs edge detection on the first imageinformation D1 and the second image information D2, and detects thepresence of the object when the edge is equal to or greater than an edgedetection threshold value th11. A first edge image E1 and a second edgeimage E2 are stored in storage 231A and 231B.

The object detector 23 also has an object recognizer 232 that performsimage recognition based on the first image information D1 and the secondimage information D2 to recognize the object. The object approachdeterminer 24 can determine that the approach of the object has beendetected on the condition that the objects (recognized objects) Brecognized by the object recognizer 232 are the same. A first recognizedobject B1 and a second recognized object B2 are stored in storage 232Aand 232B.

The object detector 23 also has a spatial frequency detector 233 thatdetects spatial frequencies F1 and F2 of the first image information D1and the second image information D2, and detects the presence of theobject when the spatial frequencies F1 and F2 are equal to or greaterthan a frequency detection threshold value th12.

At this time, for example, the first image information D1 and the secondimage information D2 are each divided into a plurality of regions, andthe edge detection or the spatial frequency detection is performed oneach region of the image information.

A first spatial frequency F1 and a second spatial frequency F2 arestored in storage 233A and 233B.

Moreover, for example, the object detector 23 detects the presence orabsence of an object first based on the image information correspondingto the lens group with the long focusing length L among the first imageinformation D1 and the second image information D2, and detects thepresence or absence of the object based on other image information onlywhen the presence of the object has been detected.

Note that, in the object detector 23, various known techniques can beused for the configuration and a series of processing in the edgedetector 231, the object recognizer 232 and the spatial frequencydetector 233. Moreover, it is also possible to adopt a configuration inwhich a part of them is omitted.

The object approach determiner 24 determines that the approach of theobject has been detected when a time difference Δt between a first timeta and a second time tb is equal to or less than an approachdetermination threshold value th1. The first time ta is when the firstimage information D1 is acquired when the object has been detected basedon the first image information D1. The second time tb is when the secondimage information D2 is acquired when the object has been detected basedon the second image information D2. When the approach of the object isdetermined to be detected, an object approach signal S1 is out.

For example, the object approach determiner 24 can determine that theapproach of the object has been detected on the condition that theregion in which the object has been detected corresponds to a regioninto which the first image information D1 and the second imageinformation D2 are divided or is a region adjacent thereto.

Moreover, for example, the object approach determiner 24 can determinethat the approach of the object is not detected in a case where theobject detector 23 detects the presence of the object based on the imageinformation corresponding to the lens group with the short focusinglength L prior to the image information corresponding to the lens groupwith the long focusing length L among the first image information D1 andthe second image information D2.

Furthermore, the object approach determiner 24 has a high-speed approachdetermination threshold value th2 that is smaller than the approachdetermination threshold value th1, and determines that the high-speedapproach of the object has been detected when the time difference Δt isequal to or less than the high-speed approach determination thresholdvalue th2.

Note that the real objects to be imaged by the imager 10 are describedas “object BT,” “object BT1,” “object BT2,” and the like, and therecognizing objects to be detected or recognized based on the imagedimage information D are described as “object B,” “object B1,” “objectB2,” and the like. However, the distinction between the real objects andthe recognizing objects is not strict.

As shown in FIG. 3, the processing unit 20 is constituted by, forexample, a CPU 101, a ROM 102, a RAM 103, a clock generator 104, anexternal I/F 105 and the like, which are connected by a bus or the like.

The central processing unit (CPU) 101 controls each part and the wholeof the object approach detection device 1 according to a program(computer program). For example, the CPU 101 can be formed byapplication specific integrated circuit (ASIC). The functions and thelike of the processing unit 20 can be realized by the executing apredetermined program by the CPU 101 and in cooperation with hardwareelements.

The read only memory (ROM) 102 and the random access memory (RAM) 103can be realized by a semiconductor, a magnetic disk, or the like, andstore control programs, application programs, data, image informationand the like. The RAM 103 is used as a working memory, and a partthereof is used as the image storage 21 and 22.

The clock generator 104 generates clocks necessary for the series ofprocessing in the processing unit 20 and provides, for example, clocksfor counting by a counter and the time stamps DTS.

The external I/F 105 receives and transmits data and signals from and toother devices. For example, the external I/F is connected to anoperation control unit and the like of a flying machine such as a droneand can transmit the object approach signal S1, the determination resultin the processing unit 20, to the operation control unit. The operationcontrol unit may perform, for example, operation for collision avoidancewhen the object approach signal S1 is received.

FIGS. 4 to 6 show imagers 10B and 10C showing other examples of the lensconfiguration of the object approach detection device 1.

In FIG. 4, the imager 10B includes a main lens 11B, a first lens group13GB constituted by a plurality of first lenses 13B, 13B and so onhaving a first focal length, and a second lens group 14GB constituted bya plurality of second lenses 14B, 14B and so on having a second focallength.

In the example in FIG. 4, the surface of the main lens 11B is the objectplane 12, and the lenses 13B and 14B are arranged along the object plane12. A first imaging element 16SB and a second imaging element 17SB arearranged on an imaging plane 15B facing the object plane 12.

In FIG. 5, an imager 10C includes a first lens group 13GC constituted bya plurality of first lenses 13C, 13C and so on having a first focallength and a second lens group 14GC constituted by a plurality of secondlenses 14C, 14C and so on having a second focal length.

In the example in FIG. 5, the first lenses 13C and the second lenses 14Care arranged on a circumferential or spherical object plane 12C.

A first imaging element 16SC and a second imaging element 17SC arearranged on a circumferential or spherical imaging plane 15C facing theobject plane 12C.

Moreover, in all of the imagers 10, 10B and 10C, the first lenses 13,13B and 13C and the second lenses 14, 14B and 14C are arrangedalternately, specifically, arranged in zigzag on the object planes 12,12B and 12C and are arranged in a matrix as a whole.

In the imager 10C in FIG. 5, shielding walls 18 are provided between thefirst lenses 13C and the second lenses 14C and the first imaging element16SC and the second imaging element 17SC to shield the optical paths tothe outside of the corresponding regions.

For example, as shown in FIG. 6, each of the shielding walls 18 may beblock-shaped provided with one light transmission hole 18 a. Each of theshielding walls 18 is inserted between the first lenses 13C (or thesecond lenses 14C) and the first imaging element 16C (or the secondimaging element 17C).

Note that the shielding wall 18 may be placoid provided with a largenumber of light transmission holes 18 a corresponding to each lens.

FIG. 7 shows an example of a flow of a series of processing for theobject approach detection in the processing unit 20.

In FIG. 7, an image such as a still image or a moving image in a targetrange is captured by the imager 10, the first image information D1 andthe second image information D2 are acquired from the image, and thetime stamp DTS is acquired at the same time. A set of the first imageinformation D1 and the second image information D2 is acquired atpredetermined time intervals and sent to the processing unit 20sequentially.

In the processing unit 20, the edge detection is performed on one set ofthe first image information D1 and the second image information D2, andthe first edge image E1 and the second edge image E2 are acquired. Thepresence or absence of an object is detected based on these edge images.When an object is detected, the time t is acquired from the time stampDTS corresponding to that first image information D1 or that secondimage information D2.

Normally, when an object approaches the imager 10 from a long distance,the first image information D1 focused by the first lens group 13G isacquired first, and the second image information D2 focused by thesecond lens group 14G is acquired thereafter. In this case, for example,the time ta is acquired for the first image information D1 and, forexample, the time tb is acquired for the second image information D2.The time ta is earlier, and the time tb is later.

In this case, the time difference Δt between the time ta and the time tbis tb−ta, and this time difference Δt is a time taken by the object tomove from the focusing length L1 of the first lens group 13G to thefocusing length L2 of the second lens group 14G. If the focusing lengthsL1 and L2 are each constant, the moving speed of the object becomesfaster as the time difference Δt becomes smaller.

Thereupon, the time difference Δt is compared with the approachdetermination threshold value th1. When the time difference Δt is equalto or less than the approach determination threshold value th1, theapproach of the object is determined to be detected, and the objectapproach signal S1 is out.

Moreover, the time difference Δt is compared with the high-speedapproach determination threshold value th2 as necessary. When the timedifference Δt is equal to or less than the high-speed approachdetermination threshold value th2, the high-speed approach of the objectis determined to be detected, and a high-speed object approach signal S2is out. The high-speed approach determination threshold value th2 issmaller than the approach determination threshold value th1 and may be,for example, equal to or less than half. For example, in a case wherethe approach determination threshold value th1 is one second, thehigh-speed approach determination threshold value th2 can be set toabout 0.5 seconds.

This will be described in more detail hereinafter.

FIG. 8A shows examples of the image information D1 and D2, and FIG. 8Bshows examples of the edge images E1 and E2 thereof.

In FIG. 8A, the image information D1 is the image captured by the firstlens group 13G and focused on the focusing length L1 of the first lensgroup 13G. The image information D2 is the image captured by the secondlens group 14G and focused on the focusing length L2 of the second lensgroup 14G.

In these image information D1 and D2, the different objects (realobjects) BT1 and BT2 are in the background, and the object BT1 isarranged farther from the imager 10 than the object BT2. The fartherobject BT1 is in focus in one image information D1 while the closerobject BT2 is in focus in the other image information D2.

The edge image E1 in FIG. 8B is the result of performing the edgedetection on the image information D1, and the edge image E2 is theresult of performing the edge detection on the image information D2.

As a method of the edge detection, there are, for example, a method ofobtaining a density gradient by differentiating the image density(luminance), a method of obtaining a density difference between adjacentpixels, and other methods. In an image of a focused object, the densitygradient and the density difference tend to increase at the edges.Therefore, for example, in a case where a ratio of a part of the areaswith large density gradient and density difference to the entire imageis equal to or greater than a certain value, in a case where the numberof pixels with large density gradient and density difference betweenadjacent pixels is equal to or greater than a certain number or certainratio, and the like, it is possible to detect the presence of thefocused object BT.

In the edge image E1 in FIG. 8B, the edges clearly appear on the focusedobject BT1, and in the edge image E2, the edges clearly appear on thefocused object BT2. Therefore, in this case, the object BT1 is detectedin the image information D1 or the edge image E1, and the object BT2 isdetected in the image information D2 or the edge image E2.

FIGS. 9A to 9C show how an object is detected from the imageinformation.

FIG. 9A shows image information D11, D12 and D13. FIG. 9B shows edgeimages E11, E12 and E13 obtained from the image information D11, D12 andD13, respectively. FIG. 9C shows frequency distribution curves ofdensity differences ΔG of the adjacent pixels in the edge images E11,E12 and E13, respectively.

In FIG. 9A, the image information D11, D12 and D13 are obtained byimaging the object (real object) BT3 arranged at the center of thescreen at different distances. Among them, in the image information D12in the center, the object BT3 is at the focusing length and focused.

In FIG. 9B, in the edge images E11, E12 and E13, the pixels after theedge detection are enlarged to be shown. Among them, the difference ofthe intensities, that is, the contrast is large in the edge image E12,and the edges are detected most frequently.

In FIG. 9C, each of the horizontal axes represents the densitydifference ΔG of each pixel, and each of the vertical axes representsthe number (pixel number) n. An appropriate position on each of thehorizontal axes is set as a threshold value thG, and the total numberNTG of the pixels with the density difference ΔG exceeding the thresholdvalue thG is checked. The total number NTG corresponds to the area atthe lower part of the curve. It is shown that the edge image E12 in themiddle has the largest total number NTG.

Therefore, for example, in a case where the threshold value thGindicating the pixels of the edges is set and the total number NTG ofpixels exceeding the threshold value thG is equal to or greater than theedge detection threshold value th11, the presence of the object B shouldbe detected in that edge image E or image information D.

Note that, in the image information D, the difference of the intensitiesbecomes larger, that is, the contrast becomes large by including a clearfocused image, and the spatial frequency F tends to be high. That is,the focused image information D has the high spatial frequency F.

Thereupon, the spatial frequency F of each of the image information D11,D12 and D13 may be detected, and the presence of the object may bedetected when the spatial frequency F is equal to or greater than thefrequency detection threshold value th12.

In this case, the spatial frequencies F1 and F2 of the first imageinformation D1 and the second image information D2 are detectedrespectively by the spatial frequency detector 233. The presence of anobject should be detected when the spatial frequencies F1 and F2 areequal to or greater than the frequency detection threshold value th12.

FIGS. 10A and 10B are diagrams showing a schematic flow of the series ofprocessing in the object approach determiner 24.

FIG. 10A shows how the object BT enters into the viewing field of theimager 10 and approaches with the time t. The imaging is performed bythe imager 10 at times t1, t2, t3, t4 and t5. The object BT ispositioned at the focusing length L1 of the first lens group 13G at thetime t2 and positioned at the focusing length L2 of the second lensgroup 14G at the time t4.

In FIG. 10B, the image information D1 and D2 imaged at each time t areschematically shown. At the time t1, the unfocused image information D1and the image information D2 substantially with nothing are obtained. Atthe time t2, the focused image information D1 and the unfocused imageinformation D2 are obtained. At the time t3, the unfocused imageinformation D1 and D2 are obtained. At the time t4, the unfocused imageinformation D1 and the focused image information D2 are obtained. At thetime t5, the unfocused image information D1 and D2 are obtained.

From these image information D1 and D2, the edge images E1 and E2 arerespectively obtained by the edge detection, and the detection of theobject BT is performed. In this example, the objects (recognizedobjects) B1 and B2 are detected from the focused image information D1 atthe time t2 and the focused image information D2 at the time t4,respectively.

As a result, the object B1 is detected at the focusing length L1 at thetime t2, and the object B2 is detected at the focusing length L2 at thetime t4. That is, the first time ta when the object B1 is detected basedon the first image information D1 is the “time t2,” and the second timetb when the object B2 is detected based on the second image informationD2 is the “time t4.” Therefore, the time difference Δt (=tb−ta) betweenthe first time ta and the second time tb is Δt=t4−t2.

Then, when the time difference Δt=t4−t2 is less than the approachdetermination threshold value th1, that is, when Δt<th1, the approach ofthe object is determined to be detected, and the object approach signalS1 is out.

Moreover, when the time difference Δt=t4−t2 is less than the high-speedapproach determination threshold value th2, that is, Δt<th2, thehigh-speed approach of the object is determined to be detected, and thehigh-speed object approach signal S2 is out.

Note that, the determination of the detection of the object approach mayinclude a case where the time difference Δt is equal to the thresholdvalues th1 or th2.

Next, various conditions for the determination of the detection of theobject approach will be described.

First, in the examples shown in FIGS. 10A and 10B, since the same singleobject BT is imaged, the detected object B1 (the first recognizedobject) and the object B2 (the second recognized object) are determinedto be the same in the object recognizer 232.

In this case, the object approach determiner 24 can determine that theapproach of the object has been detected on the condition that theobjects B1 and B2 recognized by the object recognizer 232 are the same.That is, in a case where such determination is performed, the approachof the object is determined to be not detected if the objects B1 and B2are different from each other. Therefore, the object approach signal S1is not out.

Next, FIG. 11 shows how the approach of the object is detected bydividing the region of the image information D.

In the example in FIG. 11, 300 vertical pixels and 300 horizontal pixelsare aligned in a matrix on the imaging plane 15. The imaging plane 15includes the first imaging element 16SC and the second imaging element17SC. For example, 150 vertical pixels and 150 horizontal pixels areassigned as the first imaging element 16SC and the second imagingelement 17SC, and the first image information image D1 and the secondimage information image D2 are obtained, respectively.

In the first imaging element 16SC and the second imaging element 17SC,the first image information image D1 and the second image informationimage D2 are divided into regions AE with a predetermined size. In thisexample, the images are divided into the matrix regions AE, each with 10vertical pixels and 10 horizontal pixels. In the first image informationimage D1 and the second image information image D2, the positionalrelationships of the regions AE correspond to each other.

Then, the object approach determiner 24 can determine that the approachof the object has been detected on the condition that each of thedetected regions AE corresponds to a region AE into which the firstimage information D1 and the second image information D2 are divided oris a region AE adjacent thereto in a case where the objects B1 and B2have been detected.

That is, in this case, in the second image information D2 shown in FIG.11, the approach of the object is determined to be detected only in acase where the object B2 has been detected in a region AE1 in which theobject B1 has been detected in the first image information D1, or in anyone of the eight regions AE adjacent to this region AE1 from the top,bottom, left and right. Thus, the approach of the object can be detectedwith higher accuracy.

Moreover, since the region AE in which the objects B1 and B2 have beendetected can be identified, the spatial positions of the objects B1 andB2 can also be identified.

Note that the size and setting method of the region AE in this case maybe various.

FIG. 12 shows an example of a case where the approach is determined tobe not detected even when the object is detected. In FIG. 12, the imageinformation D1 and D2 imaged at each time t are schematically shown.

That is, the imaging is performed at the times t1, t2 and t3 by theimager 10. At the time t1, no object is detected from image informationD1, and the object B3 is detected from the image information D2. At thetime t2, the object B1 is detected from the image information D1, andthe object B3 is detected from the image information D2. At the time t3,no object is detected from the image information D1, and the two objects(recognized objects) B2 and B3 are detected from the image informationD2.

In such a case, since the presence of the object B3 has been detected atthe time t1 based on the second image information D2 corresponding tothe lens group with the short focusing length L2 prior to the firstimage information D1 corresponding to the lens group with the longfocusing length L1, the approach of the object is determined to be notdetected, and the object approach signal S1 is not out.

That is, the object B3 detected based on the second image information D2is detected at all of the times t1, t2 and t3, and this is a case wherethere is an object different from the object BT which should be detectedat a position of the focusing length L2, other objects have beencrossed, or the like, leading to erroneous detection. Thus, the objectapproach signal S1 is not out herein.

What can be considered for such a situation is, for example, a casewhere the position of the imager 10 attached to the flying machine isclose to the airframe or the like and a part of the airframe is imagedor a case where the imager 10 is attached to image the lower side andthe image of the ground is always captured.

Note that, in this case, if the object B3 is not detected based on thesecond image information D2, the object B1 is detected at the time t2,and the object B2 is detected at the time t3. Thus, the time differenceΔt is t3−t2. When the time difference Δt is equal to or less than theapproach determination threshold value th1, the approach of the objectis determined to be detected, and the object approach signal S1 is out.

Moreover, the object B3 is detected based on the second imageinformation D2 at the time t1 at first. Since the object B1 is detectedat the time t2 and the object B2 is detected at the time t3, thedetermination of the presence or absence of the approach of the objectby the time difference Δt is performed on the condition that that theobject B1 and the object B2 are the same. In a case where the conditionis met, the object approach signal S1 is out.

Furthermore, if the object B3 detected based on the second imageinformation D2 is identified by the object recognizer 232 and clarifiedthat the object B3 is different from the object BT which should bedetected, the determination of the presence or absence of the approachbased on the detection of the objects B1 and B2 may be performed even inthis case.

Further, for example, in case where the object B3 is detected based onthe second image information D2 only at the time t1 and the object B3 isnot detected at the times t2 and t3, the object B3 is also considered tobe different from the object BT which should be detected. In such acase, that is, in a case where the presence of the object B3 is detectedfirst based on the second image information D2 corresponding to the lensgroup with the short focusing length L2, the detection of the object B1can be not detected for a certain period of time thereafter. In thiscase, only in a case where the presence or absence of the object isdetected first based on the first image information D1 corresponding tothe lens group with the long focusing length L1, the detection of thepresence or absence of the object based on the second image informationD2 is performed.

In addition, the detection of the object based on the second imageinformation D2 may be not performed until the object is detected fromthe first image information D1. In this way, the amount of computationis reduced, and the power consumption is reduced.

In the embodiments described above, the two image information images D1and D2 are acquired by the two imaging elements, the first imagingelement 16SC and the second imaging element 17SC, in the imagers 10, 10Band 10C. However, embodiments are not limited to this, and three or moreimage information images D may be acquired by using three or moreimaging elements, and the detection of the presence or absence of anobject and the detection of the approach of an object may be performedbased on these images D.

That is, such an imager 10D includes, for example, N (N is an integer of3 or more) lens groups which have different focal lengths from eachother and are arranged so as to image the same target object, and Npieces of image information D1 to DN, which include the first imageinformation D1, the second image information D2, the third imageinformation D3 and so on to the N-th image information DN, are acquiredby the N lens groups.

Then, for example, in the object detector 23, the presence or absence ofan object is detected based on the N pieces of image information D1 toDN. The object approach determiner 24 determines the approach of theobject has been detected when a time difference Δt between a time ta anda time tb is equal to or less than the approach determination thresholdvalue th1. The time ta is when the image information is acquired when anobject has been detected based on any one of the image information D1 toDN among the N pieces of image information D1 to DN. The time tb is whenthe image information is acquired when an object has been detected basedon other image information.

Next, a schematic flow of a series of processing in the object approachdetection device 1 will be described based on the flowchart shown inFIG. 13.

In FIG. 13, the first image information D1 is acquired by the imager 10(#11). The presence or absence of an object from the first imageinformation D1 is checked (#12). When an object is detected (YES in#12), the first time ta is acquired from the time stamp DTS or the like(#13). The second image information D2 is acquired (#14), and thepresence or absence of the object is checked (#15). When an object isdetected (YES in #15), the second time tb is acquired (#16).

The time difference Δt between the first time ta and the second time tbis obtained and compared with the approach determination threshold valueth1 (#17). When the time difference Δt is equal to or less than theapproach determination threshold value th1, the approach of the objectis determined to be detected, and the object approach signal S1 and thelike are out (#18).

According to the embodiment described above, since the presence orabsence of the approach is determined by performing the detection of anobject to obtain the time difference Δt and comparing the timedifference Δt with the approach determination threshold value th1, theamount of calculation is small, and thus the power consumption can bereduced. Incidentally, when the distance to the object is estimated asin the conventional case, the amount of calculation is large, and thusthe power consumption cannot be reduced.

Therefore, according to the object approach detection device 1 of thepresent embodiment, when the object approach detection device 1 ismounted on a small flying machine such as a drone, the flight timethereof can be made longer.

When a combination of the main lens 11, the first lens group 13G and thesecond lens group 14G is used as the imager 10, the target range of theimaging is enlarged and the viewing angle is widened so that an objectcan be detected from various directions with lightweight equipment.

In the embodiments described above, the configuration, structure,combination, size, number, material, arrangement, content of a series ofprocessing, order, threshold values th and the like of the whole or eachpart of the imagers 10, 10B and 10C, the processing unit 20 and theobject approach detection device 1 can be changed as appropriate inaccordance with the gist of the present invention.

Although embodiments of the present invention have been described andillustrated in detail, the disclosed embodiments are made for purposesof illustration and example only and not limitation. The scope of thepresent invention should be interpreted by terms of the appended claims.

What is claimed is:
 1. An object approach detection device comprising:an imager that includes a first lens group and a second lens group whichhave different focal lengths from each other and are arranged so as toimage a same target object and that acquires first image information andsecond image information imaged through the first lens group and thesecond lens group, respectively; an object detector that detectspresence or absence of an object based on the first image informationand the second image information; and an object approach determiner thatdetermines that approach of the object has been detected when a timedifference between a first time and a second time is equal to or lessthan an approach determination threshold value, the first time beingwhen the first image information is acquired when the object has beendetected based on the first image information, the second time beingwhen the second image information is acquired when the object has beendetected based on the second image information.
 2. The object approachdetection device according to claim 1, wherein the imager includes: thefirst lens group that includes a plurality of first lenses having afirst focal length; a first imaging element that receives light havingpassed through the first lens group and outputs the first imageinformation; the second lens group that includes a plurality of secondlenses having a second focal length; and a second imaging element thatreceives light having passed through the second lens group and outputsthe second image information.
 3. The object approach detection deviceaccording to claim 1, wherein the imager includes: a main lens; thefirst lens group that includes a plurality of first lenses having afirst focal length; a first imaging element that receives light havingpassed through the main lens and the first lens group and outputs thefirst image information; the second lens group that includes a pluralityof second lenses having a second focal length; and a second imagingelement that receives light having passed through the main lens and thesecond lens group and outputs the second image information.
 4. Theobject approach detection device according to claim 2, wherein theplurality of the first lenses and the plurality of the second lenses arearranged on one object plane, and the first imaging element and thesecond imaging element are arranged so as to face the object plane. 5.The object approach detection device according to claim 4, wherein eachof the plurality of the first lenses and each of the plurality of thesecond lenses are arranged alternately on the object plane and arrangedin a matrix as a whole, and a shielding wall that shields an opticalpath to outside of a corresponding region is provided between each ofthe first lenses and the second lenses and the first imaging element andthe second imaging element.
 6. The object approach detection deviceaccording to claim 1, wherein the object detector performs edgedetection on the first image information and the second imageinformation and detects the presence of the object when an edge equal toor greater than an edge detection threshold value has been detected. 7.The object approach detection device according to claim 1, wherein theobject detector detects spatial frequencies of the first imageinformation and the second image information and detects the presence ofthe object when the spatial frequencies are equal to or greater than afrequency detection threshold value.
 8. The object approach detectiondevice according to claim 6, wherein the object detector divides each ofthe first image information and the second image information into aplurality of regions and performs the edge detection on or detects thespatial frequencies of the image information in each of the regions. 9.The object approach detection device according to claim 8, wherein theobject approach determiner determines that the approach of the objecthas been detected on a condition that a region in which the object hasbeen detected corresponds to a region into which the first imageinformation and the second image information are divided or is a regionadjacent thereto.
 10. The object approach detection device according toclaim 1, wherein the object detector first detects the presence or theabsence of the object based on image information corresponding to a lensgroup with a long focusing length among the first image information andthe second image information and detects the presence or the absence ofthe object based on other image information only in a case where thepresence of the object has been detected.
 11. The object approachdetection device according to claim 1, further comprising: an objectrecognizer that perform image recognition based on the first imageinformation and the second image information to recognize the object,wherein the object approach determiner determines that the approach ofthe object has been detected on a condition that objects recognized bythe object recognizer are same.
 12. The object approach detection deviceaccording to claim 1, wherein the object approach determiner determinesthat the approach of the object is not detected in a case where theobject detector has detected the presence of the object based on imageinformation corresponding to a lens group with a short focusing lengthprior to image information corresponding to a lens group with a longfocusing length among the first image information and the second imageinformation.
 13. The object approach detection device according to claim1, wherein the object approach determiner has a high-speed approachdetermination threshold value smaller than the approach determinationthreshold value and determines that high-speed approach of the objecthas been detected when the time difference is equal to or less than thehigh-speed approach determination threshold value.
 14. The objectapproach detection device according to claim 1, wherein the imagerincludes N (N is an integer of three or more) lens groups that includethe first lens group and the second lens group, have different focallengths from each other and are arranged so as to image the same targetobject, and acquires N pieces of image information including the firstimage information and the second image information by the N lens groups,the object detector detects the presence or the absence of the objectbased on the N pieces of the image information, and the object approachdeterminer determines that the approach of the object has been detectedwhen a time difference between a time when the image information isacquired when the object has been detected based on any one piece of theimage information among the N pieces of the image information and a timewhen the image information is acquired when the object has been detectedbased on other information is equal to or less than the approachdetermination threshold value.
 15. An object approach detection methodcomprising: acquiring first image information and second imageinformation respectively through a first lens group and a second lensgroup that have different focal lengths from each other and are arrangedso as to image a same target object; detecting presence or absence of anobject based on the first image information and the second imageinformation; and determining that approach of the object has beendetected when a time difference between a first time and second time isequal to or less than an approach determination threshold value, thefirst time being when the first image information is acquired when theobject has been detected based on the first image information, thesecond time being when the second image information is acquired when theobject has been detected based on the second information.